The present invention relates to a stretch wrapping machine for wrapping a plurality of loads placed on a pallet with a plastic film in a stretched state.
For distribution and sale, products are often packed in a small unit in cartons or the like, and a certain number of packets (loads) are loaded on a pallet for shipping, cargo handling and storage.
Nevertheless, the loads on a pallet are likely to fall out of arrangement during shipping, cargo handling, storage, etc. Besides, product values may deteriorate during shipping, etc., because the pallet load may get wet by rain or the like or smeared with something like dirt. Further, some of the loads can be stolen during storage, etc.
Recently, in order to prevent palletized loads from falling out of shape and to protect them from rain, dirt, steal, etc., a polyethylene or other plastic film is wrapped around a plurality of palletized loads to provide so-called stretch wrapping.
As the stretch wrapping apparatus, there have been proposed some types of stretch wrapping machines. A turntable type stretch wrapping machine comprises a turntable for mounting a load, a carriage equipped with a feed roller for feeding a film, a mast for holding the carriage, and an elevator mechanism for raising and lowering the carriage along the mast. With a film roll set on the carriage and a pallet load placed on the turntable, the wrapping machine feeds a film along lateral surfaces of the pallet load by turning the turntable and moving the carriage upwards and downwards, so that the film is spirally wrapped around the pallet load [e.g. Japanese Patent Application Publication No. S59-9403 (JP-B-9403/1984)].
A rotary arm type stretch wrapping machine comprises a fixed table for mounting a load, a carriage equipped with a feed roller for feeding a film, an arm for revolving the carriage a round lateral surfaces of the pallet load, and an elevator mechanism for raising and lowering the carriage. With a pallet load placed on the fixed table, the wrapping machine feeds a film along lateral surfaces of the pallet load by turning the carriage around the lateral surfaces of the load and moving the carriage upwards and downwards, so that the film is spirally wrapped around the pallet load [e.g. Japanese Patent Application Laid-Open No. H8-156908 (JP-A-156908/1996)].
A rotary drum type stretch wrapping machine comprises a conveyor for carrying a long load, a carriage equipped with a feed roller for feeding a film, and a drum for rotating the carriage around lateral surfaces of the long load. With the leading end of the long load placed inside the drum, the wrapping machine feeds a film by rotating the drum while allowing the conveyor to feed the load at a fixed rate, so that the film is spirally wrapped around the long load.
Additionally, these types of stretch wrapping machine may apply a prestretch system. Such wrapping machine further comprises a stretch roller disposed opposite to a feed roller, so that a film is wrapped around a load in a prestretched state.
In the case of conventional stretch wrapping machines, operators have to perform analog volume controls in order to set various operational values such as the number of rotations of the rotation mechanism (e.g. number of turntable rotations), the feed rate of the feeding mechanism (e.g. carriage feed rate), the number of rotations of the feed roll, etc. Inevitably, the set values are heavily dependent on every operator""s sense and variable from one operation to the other. Hence, it is difficult to maintain constantly good film wrapping conditions.
Besides, operators have to put considerable time in computing control amounts such as the number of rotations of the rotation mechanism, the feed rate of the feeding mechanism, the amount of film feed, etc. based on the data related to film wrapping such as film overlap amount and film wrapping tension.
In the case of the turntable type stretch wrapping machine, when the plane geometry of the load to be wrapped is square or rectangular, the film feed amount demanded on the load side (hereinafter referred to as the film feed demand) varies during the film wrapping process. By way of illustration, as shown in FIG. 31, when a corner 9c of a load 9 is rotationally displaced from a position near a film feeder 500 as shown in FIG. 31(A) to a position shown in FIG. 31(B), the film feed demand increases along with the rotational displacement. Similar variation of the film feed demand happens in the rotary arm type stretch wrapping machine.
Where the film feed demand varies, if the feed roller rotates at a fixed speed, the tension of the film fed onto a load changes in accordance with the film feed demand. As a result, the film cannot be wrapped around the load at an even tension. Besides, because of the tension change, a film may be tensioned at a corner of the load so strongly as to be torn. Otherwise, excessive film tension may damage the corner of the load or cause the pallet load to fall out of shape.
As described above, the film feed demand varies where a pallet load has a square or rectangular plane geometry. In addition, such variation may occur due to the kinds of loads, the loading conditions, etc.
From another aspect, when a failure occurs during operation, prior art stretch wrapping machines are designed to warn an operator of the failure by flashing a lamp or the like which indicates the type of failure. Upon noticing the failure, the operator performs a recovery procedure either by looking into the manuals, etc. for a proper operation corresponding to the lamp indication or by contacting a manufacturer for instructions.
Such conventional troubleshooting procedure is troublesome and time-consuming in discovering the proper recovery operation and eventually solving the problem. When the operator has to make contact with a manufacturer to solve the problem, generally by telephone, the operator often finds difficulty in explaining the exact state of the failure to the manufacturer, and has to wait for a long time before a person in charge of maintenance can give him a proper direction.
In a stretch wrapping machine which comprises a carriage for mounting a film roll, a rotation mechanism for producing relative rotation between the carriage and an article to be wrapped, a feed mechanism for displacing the carriage relative to the article, and a controller for controlling a drive for each of the rotation mechanism and the feed mechanism, and which is arranged to feed a film to the article by providing relative rotation between the film roll-mounted carriage and the article and to wrap the film around the article by displacing the carriage relative to the article, the present invention intends to ensure constantly good film wrapping conditions for various loads, regardless of the type, shape, etc.
To achieve this object, the present invention provides a touch panel input device for setting film wrapping data into the controller and allows the touch panel input device to provide digital presentation of the set data.
In the stretch wrapping machine of this invention, the data set by the touch panel input device relate to the number of rotations of the rotation mechanism (e.g. number of turntable rotations), a film overlap amount, a film wrapping tension, and the like.
Thus, the stretch wrapping machine of this invention allows the display of the touch panel input device to provide digital presentation (e.g. digital numeric value) of set values such as the number of rotations of the rotation mechanism, the overlap amount, the film wrapping tension and the like. Therefore, any operator can easily set or switch the wrapping conditions to the same values, without personal differences. As a result, good wrapping conditions can be constantly ensured.
Besides, the touch panel input device may have a function of displaying a screen for selecting any one of a plurality of programs which are set and stored in advance.
Further, the touch panel input device may have a function of selectively displaying any one of a plurality of screens in response to a touch input, the screens including a setting screen for setting data on the number of rotations of the rotation mechanism, any one of a film overlap amount and a feed rate of the feed mechanism, and a film wrapping tension, an automatic operation screen for indicating a condition of an automatic operation and a manual operation screen for conducting a manual operation.
In addition, the controller may be arranged to monitor an occurrence of a machine failure, and, in the case of a failure, to indicate a failure point and failure details on a display of the touch panel input device.
Also, the controller may be arranged to monitor an occurrence of a machine failure, and, in the case of a failure, to supply information on a failure point and failure details to an output unit, so that the failure information can be sent from the output unit to a person in charge of maintenance via a communication network.
In a stretch wrapping machine which comprises a carriage mounted with a feed roller for feeding a film from a film roll, a rotation mechanism for providing relative rotation between the carriage and an article to be wrapped, a feed mechanism for displacing the carriage relative to the article, and a controller for controlling a drive for each of the rotation mechanism, the feed roller and the feed mechanism, and which is arranged to feed a film to the article by providing relative rotation between the film roll-mounted carriage and the article and to wrap the film around the article by displacing the carriage relative to the article, the present invention intends to ensure constantly good film wrapping conditions for various loads, regardless of the type, shape, etc.
To achieve this object, the present invention provides an input unit for setting film wrapping data into the controller. A feed rate of the feed mechanism is computed by using a set value of the number of rotations of the rotation mechanism and a set value of the film overlap amount as set by the input unit, and the computed feed rate is utilized for controlling the drive for the feed mechanism. A control amount of the feed roller is computed by using any one of a detected value of the wrapping tension and a detected value of the number of rotations of the feed roller and also using a set value of the wrapping tension as set by the input unit, and the computed control amount is utilized for controlling the drive for the feed roller.
In this stretch wrapping machine, the controller may be arranged to compute a feed rate of the feed mechanism by using a set value of the number of rotations of the rotation mechanism and a set value of a film overlap amount as set by the input unit, and to control a drive for the feed mechanism based on the computed feed rate.
In this stretch wrapping machine, the input unit may be a touch panel input device, and a display of the touch panel input device may be arranged to provide digital presentation of the set data.
In operating the stretch wrapping machine of this invention, an operator only needs to input values for the number of rotations of the rotation mechanism, the overlap amount, the film wrapping tension, etc. Accordingly, the stretch wrapping machine performs a film wrapping operation, automatically computing the feed rate of the carriage, the control amount of the feed roller (the film feed amount) and the like. Since such wrapping operation is not affected by personal differences, any operator can achieve constantly good wrapping conditions.
The stretch wrapping machine of this invention may be arranged to detect a load which is imposed on a film fed out from the feed roller to the article to be wrapped, and to constantly compute a difference between a measured value of the wrapping tension deriving from the detected value of a load and a set value of the wrapping tension as set by the input unit, thereby feedback-controlling the number of rotations of the feed roller in such a manner as to decrease the computed difference to zero.
The unit for detecting the load imposed on a film may be a load cell.
According to this arrangement, when the film feed demand varies during a film wrapping operation, the number of rotations of the feed roller is adjusted in correspondence with the varied amount. Consequently, the film wrapping tension is kept at an even level to render the film more resistant to rupture. As the load detection unit, a load cell is preferable because of its ability to detect the load (tension) imposed on the film directly and accurately as well as its simple structure.
If the stretch wrapping machine of this invention applies a prestretch system, a stretch roller is disposed opposite to the feed roller. The rotation ratio of the feed roller to the stretch roller is computed by using a set value of the stretch ratio as set by the input unit. Based on the computed rotation ratio, the number of rotations of the stretch roller is controlled.
If the feed mechanism is an elevator mechanism which displaces the carriage in upward and downward directions, the stretch wrapping machine of this invention may further comprise a top end detection unit for detecting a top end of the article. In this case, the stretch wrapping machine may be arranged to compute an upper limit of an upward travel of the carriage by using an output of the top end detection unit and a set value of an amount of top fold as set by the input unit, then to obtain a time for the carriage to reach the upper limit by using the computed upper limit and a computed value of an up-down speed of the carriage, and thereby to control the upper limit of the upward travel of the carriage.
In each stretch wrapping machine according to the above inventions, the touch panel input device may have a function of displaying a screen for selecting any one of a plurality of programs which are set and stored in advance. Accordingly, it is possible to set and store programs for performing film wrapping of a plurality of types of pallet loads in various shapes, sizes, etc. When the load subjected to film wrapping is to be changed, the wrapping conditions can be automatically switched to the conditions for a new load simply by selecting a program suitable for the new load.
The touch panel input device may have a function of selectively displaying any one of a plurality of screens in response to a touch input, the screens including a setting screen for setting data on the number of rotations of the rotation mechanism, a film overlap amount and a film wrapping tension, an automatic operation screen for indicating a condition of an automatic operation, and a manual operation screen for conducting a manual operation. This arrangement further improves the operability in the setting operation.
The stretch wrapping machine according to each of the above inventions may be arranged to monitor an occurrence of a machine failure, and, in the case of a failure, to indicate a failure point and failure details on a display of the touch panel input device. Owing to this arrangement, when a failure breaks out, an operator can easily and clearly understand the state of the failure simply by looking at the screen on the display of the touch panel input device.
The stretch wrapping machine according to each of the above inventions may be arranged to monitor an occurrence of a machine failure, and, in the case of a failure, to supply information on a failure point and failure details to an output unit, so that the failure information can be sent from the output unit to a person in charge of maintenance via a communication network. Owing to this arrangement, the failure information is directly reported to the manufacturer side, instead of being informed by an operator. Therefore, even if the operator is not familiar with the structure and operation of every part of the stretch wrapping machine, the manufacturer can understand the exact state of the failure.